Democratic presidential candidate US Sen. Bernie Sanders (I-VT) speaks during a press conference on health care on May 31, 2016 in Emeryville, California. Bernie Sanders is campaigning in Northern California ahead of the State's presidential primary on June 7th. (Photo by Justin Sullivan/Getty Images)

Bernie Sanders' campaign has condemned the media for a 'rush to judgment' in declaring Hillary Clinton the Democratic party's presumptive presidential nominee.

In response to Monday's Associated Press report that Hillary Clinton has secured the delegates needed to become the nominee, the Sanders' campaign issued a statement saying it's wrong to count the votes before July's convention in Philadelphia.

Sanders’ spokesman Michael Briggs said Mrs Clinton's support was dependent upon superdelegates who could still change their minds between now and the July convention.

Mr Briggs said: "It is unfortunate that the media, in a rush to judgment, are ignoring the Democratic National Committee’s clear statement that it is wrong to count the votes of superdelegates before they actually vote at the convention this summer.

"Secretary Clinton does not have and will not have the requisite number of pledged delegates to secure the nomination. She will be dependent on superdelegates who do not vote until July 25 and who can change their minds between now and then.

"They include more than 400 superdelegates who endorsed Secretary Clinton 10 months before the first caucuses and primaries and long before any other candidate was in the race.

"Our job from now until the convention is to convince those superdelegates that Bernie is by far the strongest candidate against Donald Trump."

Sanders has vowed to win primaries in California and beyond. Mr Sanders' supporters expressed disappointment that the calls were made before California's primary and urged the senator to continue on despite the pronouncements.

"We're going to keep fighting until the last vote is counted," said Kristen Elliott, a supporter from San Francisco who attended the rally.

Another attendee, Patrick Bryant of San Francisco, said: "It's what bookies do. They call fights before they're over."

Mr Obama called Mr Sanders on Sunday as he campaigned in California, a Democrat source told The Associated Press.

Asked if he had talked to Mr Obama, Mr Sanders said. "I have spoken to President Obama many, many times about many issues, and I really think it's not appropriate to talk about my discussions with the president. I try to keep that private."

Democrats are voting in six states on Tuesday, headlined by California, the nation's largest state, offering 475 pledged delegates, while Mrs Clinton, a former New York senator, is heavily favoured in New Jersey primary, which has 142 pledged delegates.

Mr Sanders, a self-described democratic socialist, who has won 20 states, has outlined plans to influence the party platform and try to persuade superdelegates that he would fare better than Mrs Clinton against presumptive Republican nominee Mr Trump.

Mr Sanders has previously said that Mrs Clinton should not be deemed the party's nominee because she would be relying on superdelegates - party officials and elected leaders - who do not actually vote until the Democratic National Convention.

Mr Sanders has campaigned intensively in California for more than two weeks, blanketing the state with rallies and events in 34 cities aimed at talking directly to thousands of voters at a time.

He capped the day with a concert rally featuring singer Dave Matthews and then was travelling to Los Angeles on Tuesday for the primary.